When crude petroleum oil is pumped to the surface of the earth, producers often attempt to determine the water content of the oil because water can corrode pipes and damage down-stream processing equipment. Furthermore, the water has no value relative to the oil and, in fact, can become a disposal or environmental problem when finally removed from the oil.
The accurate determination of the water content and the validation of the amount of water in crude petroleum oil is particularly important during the sale and taxation of crude petroleum oil. The owner or seller of the oil does not want to pay taxes on water and the customer does not want to pay the price of oil for water. Such determinations and validations can be conducted online and offline during petroleum processing.
Offline methods involve physically sampling the stream and analyzing it in a laboratory setting. In the petroleum industry, sampling is usually done using a composite sampler, which automatically opens a sample valve attached to a pipeline at a certain time interval to collect an aggregate sample into a sample container. The objective is to collect a representative sample of the entire lot of petroleum under consideration. After collection, the composite sample is usually taken to a laboratory. The composite sample is then divided into aliquots, or sub-divisions of the composite sample, according to the various characterizations or analysis methods being implemented.
However, composite petroleum samplers and the associated analytical methods have problems and disadvantages, such as meeting a desired accuracy for a given determination. For example, results for composite samplers are typically only available at the end of a batch or a test, and there is no recourse if something goes wrong with the sampling system during the sampling process. At the end of the sampling and analysis, only a single number is available to consider. Additionally, the exposure of personnel to hazardous liquids associated with processing the samples is undesirable. Thus, the petroleum industry has continued to seek other methods that provide the required accuracy, speed, and safety.
Accordingly, the use of rapid on-line instruments such as densitometers, capacitance probes, radio-frequency (RF) probes, and microwave analyzers to measure the water content of petroleum products is becoming more common. In addition to providing increasingly accurate determinations of water content, real-time water content measured by on-line methods provides beneficial operational advantages. Knowledge of when water becomes present in petroleum as it is being produced and the quantity of the water provides an opportunity to remove the water before it corrodes or damages a transport pipeline, storage vessel, or shipping tanker.
Additionally, real-time data may show if the water is detected in several short periods of time or if it is present across the entire load of the petroleum. The results from real-time analyzers may be used as a comparison to the results from composite samplers. On-line measurement of, for example, physical and electrical properties via instrumentation reduces the need for human involvement in the process of characterizing a multiphase fluid mixture.
However, the calibration of on-line analyzers is extremely important. It is particularly important to determine the water cut (i.e., water percentage) and the water salinity as accurately as possible during the calibration procedure. Therefore, there is a need in the art for improved apparatuses and methods for accurately determining the water cut and salinity when calibrating and online analyzer.